1. Field of the Invention
The present invention relates to imaging apparatuses and, in particular, an imaging apparatus capable of simultaneously obtaining various images.
2. Description of the Related Art
Japanese Patent Application Laid-Open No. 2010-210903 describes a focus detection optical system of a pupil-division-type phase difference detection type including paired focus detecting pixels, the pixels having a pixel with a light-shielding mask whose left half opens in a semicircular shape and a microlens formed on a front surface of a light-receiving surface and a pixel with a light-shielding mask whose left half opens in a semicircular shape and a microlens formed on a front surface of a light-receiving surface.
As depicted in FIG. 11, an image of a light beam passing through an imaging lens 100 is formed by a microlens M on the light-receiving surface of each cell of an image pickup device 160. Since a light-shielding member 161a formed on the light-receiving surface of a light-receiving cell 160a of the image pickup device 160 shields a light beam passing through a center region 100a of the imaging lens 100, only an image of a light beam passing through a peripheral region 100b of the imaging lens 100 is formed on the light-receiving cell 160a. Also, since a light-shielding member 161b formed on the light-receiving surface of a light-receiving cell 160b of the image pickup device 160 shields a light beam passing through the peripheral region 100b of the imaging lens 100, only an image of a light beam passing through the center region 100a of the imaging lens 100 is formed on the light-receiving cell 160b. 
Forming different images by pupil division is used not only for focus detection but also in a monocular stereoscopic imaging apparatus. In the monocular stereoscopic imaging apparatus, light passing though the imaging lens is subjected to pupil division, and images of a subject image passing through different regions of the imaging lens are formed at respective image pickup devices, thereby simultaneously obtaining a plurality of images.